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Photocopying

What is photocopying?

  • Broadly, photocopying is a set of techniques used to duplicate content using, among other things, light.
  • However, the contemporary colloquial use of the word ‘photocopying’ refers almost exclusively to xerography.
  • Both the word ‘xerography’ and the name ‘Xerox’ come from the Greek root­word ‘xero’, meaning ‘dry’.
  • This is because xerography is a type of photocopying method where the process doesn’t involve messy liquid chemicals.
  • Xerographic machines are in ubiquitous use around the world today to quickly and cheaply reproduce printed material.

How does xerography work?

  • Xerography has a few basic elements.
  • The first is the photoconductive surface a surface coated with a photoconductive material.
  • Such a material, when exposed to light, allows electrons to flow through it (that is it conducts electricity) but blocks them when it’s dark.
  • This surface is negatively charged by placing a thin negatively charged wire with a high voltage next to it.
  • Then, the sheet of paper to be copied is illuminated with a bright light.
  • The darker parts of the paper where something is printed don’t reflect the light whereas the unmarked parts do.
  • This reflected light is carried by lenses and mirrors to fall on the photoconductive surface.
  • In the parts of the surface where light falls, the photoconducting material will become conductive and allow the electrons near its surface to dissipate downwards (into a grounding).
  • So the parts that remain negatively charged at the end of this step will correspond to parts of the paper­to­be­copied (TBC) where something was printed.

Who invented xerography?

  • Inspired by the work of the Hungarian engineer Paul Selenyi, an American attorney named Chester F. Carlson came up with a rudimentary version of xerography by 1938.
  • Seven years later, he sold his idea to a non­profit organisation called the Battelle Memorial Institute in Ohio, where researchers refined the technique.
  • A year later, in 1946, the small New York­based Haloid Photographic Company purchased a licence from Battelle to build a machine based on the technique.
  • The company trademarked the name for this machine as the “Xerox machine” in 1948 and availed the first model for sale in 1949.
  • Haloid’s managers were responsible for coining the word ‘xerography’, replacing Carlson’s ‘electrophotography’.

Syllabus: Prelims

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